Marked electrolytic tinplate and method for producing same



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A. E. KADELL MARKED ELECTROLYTIC TINPLATE AND Filed April 10, 1952METHOD FOR PRODUCING SAME w 4 Niall! no Nov. 20,' 195.6

A LFRE D E ATTORNEY .Patented Nov. 20, 1956 MARKED ELECTROLYTIC TINPLATE AND METHOD FOR PRODUCING SAME Alfred E. Kadell, Steubenville, Ohio,assignor to National Steel Corporation, a corporation of DelawareApplication April 10, 1952, Serial No. 281,574

28 Claims. (Cl. 29--196.4)

The present invention relates to electrolytic tinplate marked in a novelmanner and relates to a novel method for producing such markedelectrolytic tinplate.

This applictaion is a continuation-in-part of my copending applicationSerial No. 229, 338, filed June 1, 1951, now abandoned.

Tinplate may be produced by the hot dip process or the electrolyticprocess. Most of the tinplate today is electrolytic tinplate and isproduced by continuously and progressively passing base metal strip,such as steel black plate, through a long electroplating line at a veryhigh rate of speed. The speed may, for example, be from a thousand totwo thousand feet per minute so that an electroplating line produces alarge quantity of tinplate in a short period of time. The strip as it ismoved through the line is first cleaned, pickled and washed and thenpassed through electroplating apparatus and both surfaces areelectroplated with tin while the strip is in contact with a bath ofelectroplating solution. The two surfaces of the strip may beprogressively plated simultaneously or one surface may be plated andthen the other surface plated. In one type of electroplating line whichis in commercial use, the strip is moved across a first series ofelectroplating cells and the bottom surface is plated, and then thestrip is moved back across a second series of electroplating cells andthe opposite surface which is now facing downwardly, is plated. Theelectro-deposited tin coating has a dull matte surface having a whitish,powdery appearance. The surface is rough and the tin while firmlyattached to the base metal is in an amorphous condition. Theelectroplated strip passing from the electroplating apparatus hasthereon electroplating solution dragged out of the electroplating bathand the plated strip is washed to remove this dragged out solution. Thewashed strip is dried or substantially dried and the drying may beeffected by passing the strip through a heated dryer, for example, or ifthe strip is rinsed with a hot rinsing solution the strip may be heatedsufficiently hot to effect drying by evaporation. The dry rinsed stripis then passed through a flow-brightening unit in which the tin isheated to a temperature above its melting point. The strip is thenquenched to solidify the tin coating. The flow-brightened tin coatinghas a smooth, bright mirror-like surface and in addition to an improvedappearance, the flow-brightened tin coatingis alloyed, at least to alimited extent, with the base metal and has a crystalline structure. Theflow-brightened coating provides better protection for the base metalthan the electroplated tin in its original condition. Theflow-brightened strip may then be coated with a film of oil and thencoiled into large rolls or coils at the finishing end of the line. Thestrip before being coiled and oiled may be cathodically treated andWashed. The coils are subsequently cut into sheets from which are formedthe final products, such as food containers.

Very large quantities of electrolytic tinplate are utilized in industryand millions of pounds of tin are required each year to satisfy thetinplate requirements for the food and other industries. A large portionof this electrolytic tinplate is used in containers where the tincoating on the interior surface protects and prevents contamination ofthe contents. The tin coating on the exterior surface enhances theappearance of the container and while having a tin coating on theexterior surface is important and highly desirable both to enhance theappearance and to protect the container, the quantity of tin on thisexterior surface frequently need not be as great as the quantity of tinon the interior surface. In the present days of tin shortages a savingin tin is quite important. The commercial tinplate now produced has thesame amount of tin on each surface and a large saving of tin wouldresult if the opposite surfaces could be coated with differentquantities of tin. The tin coating could be thinner on the surface whichneeds less protection, such as the exterior surface of containers.

If electrolytic tinplate were produced with different weights of tin onthe surfaces a saving in tin could be effected but this in turn wouldraise a serious problem when using the tinplate. Flow-brightenedtinplate has a bright, mirror-like surface and there is no appreciablevisible difference between a surface having a relatively thinner coatingand one having a relatively thicker coating. Thus, the manufacturer whoproduces the containers or other products would not be able to readilydetermine which surface of a sheet of tinplate should form the exterioror interior surface of a container. Marking tinplate by means of a dieor other apparatus that deforms the metal is not satisfactory as itdestroys a portion of the sheet that is marked. Marking ink cannot beutilized as the ink tends to spread and smear at the high speedsinvolved. The ink may be removed by the subsequent treatments, such asthe cathodic electrolytic treatment and the washing and oilingtreatments. Ink tends to transfer from the marked to the unmarkedsurface during coiling. In addition, ink tends to darken when thetinplate is subsequently coated with lacquer and baked and presents anunsightly appearance. Accordingly, customary marking procedures are notsatisfactory or desirable for tinplate.

I have discovered a novel method of producing a novel, flow-brightenedelectrolytic tinplate that is marked. This marking can be utilized todifferentiate one surface of a sheet from the other surface or for anyother purpose of designation.

Marking is effected bypassing the electroplated strip throughflow-brightening apparatus and heating and flowbrightening the tincoating on the strip while interfering with the flow-brightening of thetin coating located in the marking Zones so that these portions of thetin coating will have different, visible, light reflectingcharacteristics than the flow-brightened coating on the remaining areaof the surface. Preferably these marking zones extend eithercontinuously or at closely spaced intervals I along the length of thestrip so that when the strip is cut into sheets, each sheet will have onone surface at least a few of these zones. The marking zones may bearranged in a repeating pattern extending along the length of the stripand may be in the shape of lines extending longitudinally along ortransversely across the strip surface. In the arrangement which willhereinafter be described in detail, the marking zones are arranged inintersecting lines extending diagonally across the sheet. But otherarrangements obviously can be used. Preferably these lines arerelatively faint so as not to be readily noticeable under normalconditions of lighting, but readily visible when viewed under a stronglight, particularly when the light source and the tinplate are arrangedso that light is reflected from the marked surface to the eye at acuteangles. The person or persons responsible for properly positioning thetinplate can readily distinguish the marked surface, while the markedsurface will not be particularly noticeable or present an undesirableappearance to the casual observer. Relatively faint lines can be coveredreadily by a decorative coating. More pronounced lines can be coveredbut a heavier coating of greater opacity is required.

Interference with the flow-brightening of tin coating in the markingzones is effected so that the tin in the marking zones isflow-brightened in such a manner as to present a differential visualappearance. The flow-brightening may be affected by partially blockingthe heat away from the marking zones or by absorbing some of the heatdirected against the marking zones or by a chemical reaction between aforeign material and the tin coating so as to produce a tin coating inthe marked areas having less gloss or a slightly duller appearance. Onthe other hand, the flow-brightening may be affected by increasing thefluidity of the tin in these zones by means of a fluxing action whichmay cause the tin coating to reflect less light or to diffuse thereflected light so as to have a duller or darker appearance.Interference may be effected by a combination of those methods. Themarking zones will have different visible light reflectingcharacteristics than the remaining portions of the surface and mayreflect less light or may diffuse the light in a different manner so asto appear darker to the naked eye, particularly when the marked tinplateis held at an angle to the light source.

While the marking zones on the surface of the tinplate have differentlight reflecting characteristics than the remaining portion of thesurface area, the tin located in these zones is not in its originalcondition having a matte surface but is in a flow-brightened condition.

Interference with the flow-brightening may be carried out by decreasingflow-brightening of the tin in the marking zone. A decrease offlow-brightening may be effected by physically blocking some of the heataway from the zones so that less heat reaches these zones and this maybe effected by applying a foreign material to the marking zones beforethe flow-brighting operation, such as a transparent lacquer or sizing,that will partially insulate the zones. A reduction in flow-brighteningalso can be effected by adding a material to the zones before theflow-brighting operation so as to reduce the amount of heat applied tothe tin coating through absorption of heat by vaporization of thematerial. Palm oil, for example, may be used for this purpose.Interference also may be effected by applying to the marking zones aforeign material that will chemically react with the tin. An acid oracidic compound that will have an etching action on the coating duringthe flow brightening operation may be used for this purpose.

Interference with the flow-brightening of the tin in the marking zonescan be effected by increasing the flowbrightening effect on the tin. Anincrease of the flowbrightening of the tin can be effected by applying afluxing agent to the surfaces to be marked prior to the flowbrighteningoperation. The fluxing agent may increase the fluidity of the tin andthis in turn may increase the tendency of the tin in these areas tocollect in droplets so that the flow-brightened tin coating will reflectlight differently than the remaining portion of the surface areadepending to a limited extentupon the fluxing agent used and thetemperature to which the tinplate is heated. The marking zones may beslightly brighter than the remaining area or may have a slightlyroughened surface so as to diffuse the light and present a relativelydull, different visible appearance. It is to be noted that a materiallike palm oil has two effects. It has a limited etching action and alsotends to reduce the amount of heat reaching the tin at least partiallyas a result of its partial vaporization. Thus, a combination of thesevarious methods may be used when interfering with the flow-brighteningin the marking zones.

The present invention will become more apparent from the followingdescription taken with the accompanying drawings, in which:

Figure l is a diagrammatic representation of improved apparatus forcarrying out the principles of the present invention;

Figure 2 is an enlarged fragmentary view taken as indicated by line 2-2of Figure 1;

Figure 3 is an enlarged sectional view taken along line 3-3 of Figure 2;and,

Figure 4 is an enlarged view of a portion of the strip illustrating onearrangement of the marking zones.

Referring more particularly to the drawings, Figure 1 illustrates theessential portions of one type of an improved elcctroplating line forcarrying out the method of the present invention. The electroplatingline includes apparatus ill or electroplating the bottom surface ll ofstrip S with a coating of tin and other apparatus 12 for electroplatingthe opposite surface 13 of the strip S with a coating of tin. Theapparatus for electroplating the bottom surface includes a series ofsimilar electroplating cells 15. Between each two cells It. and at theentry and exit ends of the series of cells, there are a pair of stripengaging rolls i6 and 17. One of the rolls, usually the upper roll, is acontact roll and is connected to one side of the source of theelectroplating current so as to connect the strip S to a source ofelectroplating current as a cathode. The other roll, roll 17 is backuproll holding the strip in contact with the upper roll 16. The rolls mayor may not be driven. The cells 15 are of the type which contain a bathof electroplating solution and a plating anode (not shown) connected tothe source of electroplating current as an anode. The strip S movesacross the top of the cells where the bottom surface it is in contactwith the electroplating solution in each cell. As the strip moves acrossthe series of cells, a coating of tin is applied to the bottom surface11.

At the entry and exit ends of the series of cells 15 and between eachtwo cells there is a collecting tray 19 which collects the solutionflowing out of the cells and this solution is returned through piping26) to a collection tank, not shown, and then is pumped back into thecells through pipe 21. As the strip leaves the lower apparatus 10, itpasses around a roll 23 and then up and around an upper roll 24 and thenacross the upper electroplating apparatus for electroplating theopposite surface 13 which is now facing downwardly. The apparatus 12 issimilar to the apparatus 10 and includes a plurality of similarelectroplating cells 26 across which the strip is moved in contact withthe electroplating solution in each cell whereby the bottom surface 12is plated with coating of tin. At each end of the series of cells 26 andbetween each two cells, there is a pair of rolls withthc upper roll 27being a contact roll and the lower roll a backup roll 28 to connect thestrip to a source of electroplating current as the cathode. From theupper series of cells 12, strip passes around roll 3i then up and aroundroll 31 to a washer 32. The washer 32 may be any suitable type andwashes the strip to remove the residual electroplating solution that ison the strip and that has been dragged out of the electroplating cells.The strip then passes through a dryer 33 which dries the strip. Thedryer 33 may be of any suitable type for applying sulTtcient heat to thestrip to dry the metal. Where the wash water used in washer 32 is at anelevated temperature, there may be sufficient heat in the strip to drythe strip before the strip passes to the reflowing or flowbrighteningapparatus 34, As the strip moves through the flowbrightener, the stripis heated to a temperature above the melting point of tin and heat maybe applied to the strip in any suitable manner. From the bottom of theflow-brightener, the strip passes down into quench tank 35 containing abath 36 of quench liquid such as water.

In the quench tank 35, the strip passes around a roll- 37 and from thetank up to roll 38. The strip then passes to units for subsequentlytreating the strips and to the usual coiler.

In the apparatus described above the strip is first plated on onesurface with a protective coating of tin and is then plated on theopposite surface with a protective coating of tin, washed, dried,flow-brightened and quenched. Other types of plating apparatus may beused and both surfaces may be plated simultaneously. United StatesPatent No. 2,317,242 to W. S. Allen et al., for example, illustratesanother type of apparatus which may be used.

Any suitable type of flow-brightener may be used and the strip and itstin coating may be electrically heated, or may be heated by radiantheaters or'may be heated in a hot, inert atmosphere. In general, liquidscannot be used as the heating medium as liquid tends to remove theforeign material. Flow-brightening units are well known to those skilledin the art.

In accordance with the present invention, one surface of the strip maybe plated with a thinner coating of tin than the opposite surface. Inthis instance, it is the bottom surface which is plated with the thinnercoating and this difference in coatings may be eifected in various waysas, for example, by utilizing a lower current density in the cells 15than is used in cells 26, or by using fewer cells 15 or in any othersuitable manner.

The weight of tin present on tinplate is usually referred to as acertain weight of tin per base box. A base box of tinplate contains217.78 sq. ft. of tinplate. As tinplate is coatedon both surfaces withtin the amount of tin per base box is distributed over an area of 435.56sq. ft. Thus, the expression one pound tinplate refers to tinplatehaving one pound of tin per base box and the tin is distributed over anarea of 435.56 sq. ft. As used, hereinafter, the terms or expressionssuch as, one pound tinplate or one pound of tin per base box refers totinplate which has this amount of tin distributed over i both sides ofthe tinplate throughout an area of 435.56 sq. ft. The expression onepound tin one side or one pound of tin per base box, one side refers tothe quantity of tin distributed over one surface of a base box oftinplate or over an area equal to 217.78 sq. ft. Thus, one poundtinplate or one pound tinplate per base box is equivalent to one-halfpound tinplate, one side, or onehalf pound tinplate per base box, oneside.

In the present instance it is the bottom surface that is coated with thethinner coating. The difference in coating weights may be varied andwill depend upon the use to which the tinplate is to be put. Forexample, instead of producing one pound per base box tinplate, tinplatemay be produced having a half pound per base box, one side, and .25pound tin per base box, reverse side. Thus, the one side of the tinplatewill be protected with the same thickness of tin that is present on onepound tinplate. The tin coating on the other or reverse side of thetinplate will only have a thickness equal to the usual half poundtinplate. This effects a savings of 25% of tin which would normally beused to produce this tinplate. Lesser or greater savings can be effectedand savings up to 50% or higher in tin can be made. Thus, where, forexample, a company produces over 20,000,000 base boxes of tinplate peryear, a saving of /1 pound of tin per base box would amount to over5,000,000 pounds of tin in a year. Thus, a relatively slight savings intin per base box is quite important and highly desirable.

In accordance wit-h the present invention, the flowbrightening of thetinplated strip in the flowbr-ightener 34 is interfered with so as toproduce a tinplate having tin coating in minor zones of one surface thathave different visible light reflecting characteristics than thehowbrightened tin coating in the remaining area of said surface. Theflow brightened tinplate in these minor or marking zones appearsslightly darker to the naked eye. In the procedure shown in Figure 1, itis the bottom surface that has the thinner coating and preferably,

6 though not necessarily, it is the surface having the thinner coatingthat is marked. As shown more fully in Figures 2 and 3, the strip Swhich has been washed and which has thereon a matte surface finish ispassed between a pair of rolls 40, 41. These rolls are rotatablysupported in any suitable manner. The lower roll is mounted above a tank42 containing a bath of liquid 43. In the tank 42 there is mounted awick 44 which extends down into the bath 43 and which contacts thesurface of the roll 41. The roll 41 may be made of rubber or any othersuitable material and have thereon raised portions with the raisedportions being arranged in lines 45. These raised portions or lines 45are quite narrow and extend about the periphery of the roll 41. Thus, asthe strip moves between the lower roll 41 and the upper roll 49 whichpresses the strip against the lower roll, the lower roll 41 rotates anddeposits liquid from bath 43 onto the surface of the strip in zones.These zonesare arranged as intersecting lines extending diagonally ofthe sheet. As the strip subsequently moves through the flowbrightener34, the liquid or foreign material deposited on the surface by roll 41interferes 'With the flow-brightening so as to produce a flow-brightenedtin coating in the marking zones that has a different light reflectingcharacteristic than the remainder of the sheet. The bottom surface ofthe sheet will be marked with faint lines 47 as indicated in Figure 4.These marking lines or zones may reflect less than the remainingunmarked zones between the lines '47 or the tin coating in the markingzones 47 may diffuse the light differently than the remainder of thecoating.

Liquid bath 43 may contain any suitable material. If, for example, thebath 43 is palm oil, the palm oil will be deposited in the minor markingzones on the bottom surface of the strip. As the strip moves through theflow-brightener 34, a portion of the palm oil will be vaporized and thisheat of vaporization will reduce the amount of heat reaching thetinplate in the mark-ing zones 47 so that the tinplate in the markingzones 'will be heated to a lower temperature than the tin on theremainder of the surface. Palm oil also is believed to have some fluxingor etching action on the tin surface. Palm oil contains some higherfatty acids and it is believed that these acids may react 'with the tinsurface, that is, etch the tin surface. 'Th-us, palm oil acts to bothreduce the amount of heat applied to the tin coating in the markingzones 47 and acts to slightly etch the surface. The bath 43 may containa tin reactive fluxing agent and may be for example, an aqueous solutionof sal ammoniac. The water will be evaporated in the flowbrighteningzone and the residual sal ammoniac will act as an etching and fluxingagent to both increase the fluidity of the tin in the marking zone andto lightly etch the surface of the tin in the marking zone. The tin inthese mark-ing zones -will diffuse the light and will be visiblydifferent from the remainder of the tin coating. This difference isparticularly noticeable when the plate is held at an angle to the lightso that the plate is viewed by light reflected at an acute angle. Themarking zones appear darker than the remainder of the tinplate.

Other heat absorbing materials or tin reactive materials or combinationsof these ingredients may be used to form the bath 43. Preferably themarking material is tin reactive acidic material that has at least aslight etching action on the tin coating as better results have beenobtained with such materials as compared to non-etching materials suchas cottonseed oil or glycerine, although the last mentioned materialsmay be used. The tin reactive, acidic material may be a mineral acid,for example, hydrochloric acid or hydrofluoric acid, or may be an acidsalt of a metal such as sodium bifluoride. The strongly acid materialsshould be used in diluted form and may be diluted with Water or waterand glycerine. For example, an aqueous solution of hydrochloric acidcontaining 2%, or less, of acid may be used. Where the tin reactivematerial is an acid salt, then only a few ounces, or less, per gallonmay be needed. The preferred concentration will depend on the reactivityof the salt, the amount of film applied and other factors. The markingliquid comprising an aqueous solution of a tin reactive acid salt maycontain or more, acid salt, although good results have been obtainedwith solu tions containing 1%, and less, of acid salt. Preferably themarking material should not have too strong an etching action as thereis a tendency for such a material to shorten the shelf life of thetinplate. The term shelf life refers to the period over which tinplatecan be stored without deterioration sufficient to affect its value. Forthis reason mineral acids and tin reactive acid salts of metals are usedin diluted form with the degree of dilution depending upon the strengthof the acid or acid salt. While the term etching has been used, thisetching is slight and the etched surface appears to have a smoothsurface so that the etched effect does not produce a rough appearingsurface but does affect light reflecting characteristics of the tincoating in the marking zone.

()ther materials may be used for marking the tinplate. Alcohol and salammoniac may be used although a mixture of alcohol, water and salammoniac is better. A tin reactive material may be added to palm oil orglyccrine, for example, stearic acid may be added to palm oil and asmall amount of hydrochloric acid may be added to glycerine to form thematerial for bath 43.

Where the bath 43 includes a liquid such as water which evaporates inthe flow-brightening zone and a tin reactive agent, marking isapparently effected by a dual action. The liquid reduces the heatreaching the tinplate in the marking zone both by blanketing the surfaceand blocking the heat and by absorbing heat of vaporization. While allof the tin coating in the marking zone is flowbrightened this reductionin heat tends to produce a tin coating having visibly different lightreflecting characteristics. In addition, the flow-brightening of the tincoating in the marking zone is interfered with by the residual tinreactive material which lightly etches the surface, particularly Wherethe tin reactive material is an acid salt that does not evaporate ordecompose in the flow-brightening zone without reacting with the surfaceof the tin coating. Where the bath contains a tin reactive acid salt, itis believed that a residue of this acid salt may at times remain on thetin coating in the marking zone, probably in the form of a salt of tin.If such a salt remains on the marking zone, the salt cannot be seen bythe naked eye although it may affect the light reflectingcharacteristics. The quenching medium may remove any such residual salt.As such an acid salt is used in a diluted form and as a very thin filmis applied to the marking zone, only a minute amount of salt residue canbe present on the tin coating in the marking zone. The etching is quitelight and the only visible effect of such etching is to increase thedifference in light reflecting characteristics. No pits or depressionscan be seen. If pits or depressions were formed having a size sufficientto be distinguished by the naked eye, the protective character of thetin coating would be greatly reduced. Accordingly, the term lightlyetched is intended to cover that condition where the material applied tothe marking zone reacts with the surface of the tin coating sufficientlyto affect the light reflecting characteristics of the surface but notsufficiently to form pits or depressions individually visible to thenaked eye.

A material may be used for bath 43 which will block part of the heatdirected toward these minor zones on the strip surface. For example, thebath 43 may be made up of a substantially clear sizing coating oflacquer of the type used for priming tinplate for receiving a protective or decorative coating of lacquer or paint. This sizing orlacquer applied to the strip S by roll 41 will block or prevent some ofthe heat reaching the marking zones but permits suflicient heat to reachthese zones so that the tin is flow-brightened. Thus, the tin coating inthe marking zones receives less heat and has less gloss than the tincoating in the remaining area of the surface.

When interference with the flow-brightening is effected by applying aforeign material to the surface of the tinplate, I prefer to employ amaterial that will subsequently be removed by the quench bath 36 orwhich may readily be removed by washing with a suitable liquid which maybe different than is used in the quench bath. Many of the materialspreviously mentioned are water soluble and are removed in the quenchbath.

As previously pointed out the bottom surface is preferably marked sothat the marking area constitutes only a very small portion of theentire area. In addition, the marking zones are preferably relativelynarrow and laiut. While the marking zones may be relatively wide andquite pronounced, particularly where this surface in the finishedproduct is completely covered as by a paper label, it is preferable thatthe marking zones not be pronounced so that they will not be noticed bythe casual observer and so that they may be readily covered andobliterated by a lacquer having a low hiding power.

The present invention has been described for marking electrolytic striptinplate having different weights of the tin on the opposite surfaces todistinguish these surfaces. The present invention may be used formarking electrolytic tinplate of other types and for other purposes. Thestrip may be plated on only one surface and the marking may be used toindicate batch or lot number, coating weight or for any other purpose.The marking zones may be arranged as numerals or letters or suitableindicia of predetermined configuration and the spacing between repeatingmarks, either along the length or across the breadth of the strip, maybe varied over a Wide range.

When producing strip tinplate having a tin coating of one weight on onesurface and a tin coating of a different on the other surface, it may bedesirable to interfere with the flow-brightening of an entire one of thecoatings. This will result in one flow-brightened coating havingdifferent light reflecting characteristics than the otherflow-brightened coating. The surface of the one coating will diffusereflected light differently and appear slightly darker than the othercoating. This may be accomplished by applying, for example, an aqueoussolution of a tin reactive acid salt to the entire surface of onecoating before passing the strip through the flow-brightening zone. Atleast at times. the strip tinplate is cut into small pieces or blanksand if the entire surface of one coating is marked there is no chancethat the blank will not be marked and be improperly positioned forsubsequent fabrication.

I claim:

1. In the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositing a coating of tin onat least one surface of the strip while in contact with a bath ofelectroplating solution containing electrolyte, the tin coating in thedeposited condition having a matte surface, passing the strip from theelectroplating zone and rinsing the strip to remove residualelectroplating solution dragged out of the electroplating zone, thesteps comprising passing the rinsed strip through a flowbrightening zoneand melting and flow-brightening the tin coating, and selectivelyinterfering with the flowbrightening of the tin coating located in amarking zone of predetermined pattern and constituting only part of thetotal area of the tin coating to produce a flow-brightened tin coatingsurface in the marking zone having visibly different light reflectingcharacteristics than the flow-brightened tin coating surface outside ofthe marking zone to mark the tin coating surface.

2. In the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositing a coating of tin onat least one surface of the strip while in contact with a bath ofelectroplating solution containing electrolyte, the tin coating in thedeposited condition having a matte surface, passing the strip from theelectroplating zone and rinsing the strip to remove residualelectroplating solution dragged out of the electroplating zone, thesteps comprising passing the rinsed strip through the flow-brighteningzone and heating and melting the tin coating while the tin coating isdisposed in a gaseous atmosphere and thereby flow-brightening the tincoating, and selectively reducing the amount of heat applied to the tincoating located in a marking zone of predetermined pattern andconstituting only part of the total area of tin coating and therebyinterfering with the flow-brightening of the tin coating in the markingzone to produce a flow-brightened tin coating surface in the markingzone having visibly different light reflecting characteristics than theflowbrightened tin coating surface outside of the marking zone to markthe tin coating surface.

3. In the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositing a coating of tin onat least one surface of the strip while in contact with a bath ofelectroplating solution containing electrolyte, the tin coating in thedeposited condition having a matte surface, passing the strip from theelectroplating zone and rinsing the strip to remove residualelectroplating solution dragged out of the electroplating zone, thesteps comprising passing the rinsed strip through a flow-brighteningzone and melting and flow-brightening the tin coating, selectivelyapplying a liquid film to the tin coating located in a marking zone ofpredetermined pattern and constituting less than the total surface areaof the tin coating, the liquid film being applied to the rinsed stripbefore the strip passes into the flow-brightening zone and therebyinterfering with the flow-brightening of the tin coating in the markingzone to produce a flowbrightened tin coating surface in the marking zonehaving visibly different light reflecting characteristics than theflow-brightened tin coating surface outside of the marking zone to markthe tin coating surface.

4. In the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositing a coating of tin onat least one stuface of the strip while in contact with a bath ofelectroplating solution containing electrolyte, the tin coating in thedeposited condition having a matte surface, passing the strip from theelectroplating zone and rinsing the strip to remove residualelectroplating solution dragged out of the electroplating zone, thesteps comprising passing the rinsed strip through a flow-brighteningzone and melting and flow-brightening the tin coating, selectivelyapplying a liquid film to the tin coating located in a marking Zone ofpredetermined pattern and constituting less than the total surface areaof the tin coating, the liquid film being applied to the rinsed stripbefore the strip passes into the flow-brightening zone, at least part ofthe liquid in the film being vaporized in the flow-brightening zone, andthereby interfering with the flow-brightening of the tin coating locatedin the marking zone to produce a flow-brightened tin coating surface inthe marking zone having visibly different light reflectingcharacteristics than the' flow-brightened tin coating surface outside ofthe marking zone to mark the tin coating surface.

' 5. In the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositing a coating of tin onat least one surface of the strip while in contact with a bath ofelectroplating solution containing electrolyte, the tin coating in thedeposited condition having a matte surface,

passing the strip from the electroplating zone and rinsing the strip toremove residual electroplating solution dragged out of theelectroplating zone, the steps comprising passing the rinsed stripthrough a flow-brightening zone and melting and flow-brightening the tincoating, selectively applying a liquid film to the tin coating locatedin a marking zone of predetermined pattern and constituting less thanthe total surface area of the tin coating, the liquid film being appliedto the rinsed strip before the strip passes into the flow-brighteningzone and including Water and a tin reactive acid salt, the water beingevaporated in the flow-brightening zone and the acid salt etching thesurface of the tin coating to thereby interfere with theflow-brightening of the tin coating in the marking zone to produce aflow-brightened tin coating surface in the marking zone having visiblydifferent light reflecting characteristics than the flowbrightened tincoating surface outside of the marking zone to mark the tin coating.

6. In the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositing a coating of tin onat least one surface of the strip while in contact with a bath ofelectroplating solution containing electrolyte, the tin coating in thedeposited condition having a matte surface, passing the strip from theelectroplating zone and rinsing the strip to remove residualelectroplating solution dragged out of the electroplating zone, thesteps comprising passing the rinsed strip through a flow brighteningzone and melting and flow brightening the tin coating, and selectivelyinterfering with the flow brightening of the tin coating located in amarking zone of predetermined pattern and constituting only part of thetotal area of the tin coating by applying a tin reactive agent to thetin coating in the marking zone after the strip has been rinsed andprior to passing the strip through the flow brightened zone and therebylightly etching the tin coating in the marking zone during flowbrightening of the tin coating to produce a flow brightened tin coatingsurface in the marking zone having visibly different light reflectingchraacteristics than the flow brightened tin coating surface outside ofthe marking zone to mark the tin coating surface.

7. The method claimed in claim 6 in which the tin reactive agent is anacid salt.

8. The method claimed in claim 6 in which the tin reactive agent is atin fluxing agent.

9. In the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositinga coating of tin onat least one surface of the strip while in contact with a bath ofelectroplating solution containing electrolyte, the tin coating in thedeposited condition having a matte surface, passing the strip from theelectroplating zone and rinsing the strip to remove residualelectroplating solution dragged out of the electroplating zone, thesteps comprising passing the rinsed strip through a flow brighteningzone and melting and flow brightening the tin coating, and selectivelyinterfering with the flow brightening of the tin coating located inmarking zones of predetermined pattern and constituting only part of thetotal area of the tin coating to produce in the marking zones a flowbrightened tin coating having visibly different light reflectingcharacteristics than the flow brightened tin coating outside of themarking zones with the tin coating in the marking zones diffusing thelight more and appearing relatively duller than the portion of the tincoating outside of the marking zones.

10. The method of continuously marking electrolytic tinplated strip asclaimed in claim 9 in which the marking zones are arranged in a patternrepeating along at least one dimension of the surface of the tincoating.

11. The method of continuously marking electrolytic 11 tinplated stripas claimed in claim which includes arranging the marking zones asintersecting lines.

12. The method of continuously marking electrolytic tinplated strip asclaimed in claim 11 in which the intersecting lines intersect each otheron the diagonal with the intersecting lines defining therebetweendiamond shaped areas of flow brightened tin coating.

13. The method of continuously marking electrolytic tinplated stripclaimed in claim 9 in which a film of liquid including palm oil isapplied to the marking zones prior to passing the rinsed strip throughthe How brightening zone.

14. The method of continuously marking electrolytic tinplated strip asclaimed in claim 9 in which a trans parent film is applied to themarking zones before the rinsed strip is passed through the flowbrightening zone and in which transparent film is not evaporated as thestrip is passed through the flow brightening zone.

15. The method of continuously marking electrolytic tinplated strip asclaimed in claim 9 which includes applying an aqueous solution of a tinreactive acid salt to the marking zones prior to passing the rinsedstrip through the flow brightening zone, the water being evaporated asthe strip moves through the flow brightening zone whereby the tincoating passing from the flow brightening zone has an acid salt residueon the surface in the marking zones and is lightly etched by the acidsalt.

16. In the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositing a coating of tin onthe two sides of the base metal strip, the coating of electroplated tinon one side of the strip being relatively thinner and on the other siderelatively thicker, both of the tin coatings in the deposited conditionhaving a matte surface, passing the strip from the electroplating zoneand rinsing the strip ti remove residual electroplating solution draggedout of the electroplating zone, the steps comprising passing the rinsedstrip through a flow brightening zone and melting and flow brighteningthe tin coatings, and selectively interfering with the how brighteningof one of the tin coatings located in marking zones of predeterminedpattern and constituting only part of the total area of the one tincoating to produce a flow brightened tin coating surface in the markingzones hav ing visibly different light reflecting characteristics thanthe flow brightened tin coating surface outside of the marking zones tomark the one tin coating.

17. The method of continuously marking electrolytic tinplated strip asclaimed in claim 16 in which the tin coating in the marking zonesdiffuses the light more and appears duller than the tin coating surfaceoutside of the marking zones.

13. The method of continuously marking electrolytic tinplated strip asclaimed in claim 17 in which the marking zones are on the thinnercoating.

19. The method of continuously marking electrolytic tinplated strip asclaimed in claim 13 which includes arranging the marking zones as lines.

20. The method of continuously marking electrolytic tinplated strip asclaimed in claim 19 in which the lines are arranged as intersectinglines, intersecting each other on the diagonal.

21. in the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositing a coating of tin onthe two sides of the base metal strip, the coating of electroplated tinon one side of the strip being relatively thinner and on the other siderelatively thicker, both of the tin coatings in the deposited conditionhaving a matte surface, passing the strip from the electroplating zoneand rinsing the strip to remove residual electroplating solution draggedout of the electroplating zone, the steps comprising passing the rinsedstrip through a flow brightening zone and melting and flow brighteningthe tin coatings, and selectively interfering with the fiow brighteningof at least a portion of one of the tin coatings located in a markingzone of predetermined pattern to produce a flow brightened tin coatingportion having different light reflecting characteristics than theremaining portion of the tin coatings.

22. In the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositing a coating of tin onthe two sides of the base metal strip, the coating of electroplated tinon one side of the strip being relatively thinner and on the other siderelatively thicker, both of the tin coatings in the deposited conditionhaving a matte surface, passing the strip from the electroplating zoneand rinsing the strip to remove residual electroplating solution draggedout of the electroplating zone, the steps comprising passing the rinsedstrip through a flow brightening zone and melting and flow brighteningthe tin coatings, and selectively interfering with the flow brighteningof the entire tin coating on one side of the strip to produce a flowbrightened tin coating having different light reflecting characteristicsthan the flow brightened tin coating on the other side of the strip.

23. in the method of continuously marking electrolytic tinplated strip,which tinplated strip is produced by passing base metal strip across anelectroplating zone and electrolytically depositing a coating of tin onthe two sides of the base metal strip, the coating of electroplated tinon one side of the strip being relatively thinner and on the other siderelatively thicker, both of the tin coatings in the deposited conditionhaving a matte surface, passing the strip from the electroplating zoneand rinsing the strip to remove residual electroplating solution draggedout of the electroplating zone, the steps comprising passing the rinsedstrip through a flow brightening zone and melting and flow brighteningthe tin coatings, and selectively interfering with the fiow brighteningof the entire tin coating on one side of the strip to produce a flowbrightened tin coating which diffuses reflected light more and appearsduller than the tin coating on the other side of the strip.

24. Electrolytic sheet tinplate having on at least one side a coating ofelectroplated tin in the flow brightened condition, the tin coatinghaving a marking zone on the surface covering less than the entiresurface area of the tin coating, the physical condition of the surfaceof the tin coating in the marking zone being different from andcharacterized by visibly different light-reflecting characteristics thanthe surface of the tin coating outside of the marking zone, the physicalcondition of the surface of the marking zone being the result ofinterference with flow brightening.

25. The electrolytic sheet tinplate claimed in claim 24 in which the tincoating surface outside of the marking zone has a bright substantiallymirror-like appearance and the tin coating surface in the marking zonediffuses the light more and appears relatively duller than the tincoating outside of the marking zone.

26. The electrolytic tinplate of claim 24 which has a transparent filmcovering the marking zone only.

27. Electrolytic sheet tinplate having on one side a coating ofelectroplated tin in a flow brightened condition presenting a bright,light-reflective surface and having on the other side a coating of tinin the flow brightened condition presenting a light-reflective surface,one of the coatings being heavier than the other coating, at least aportion of the tin coating on the said other side of the sheetpresenting a surface having a physical condition different from andcharacterized by visibly different light-reflecting characteristics thanthe surface of the tin coating on said one side of the sheet, thephysical condition of the surface of at least the portion of the otherside of the sheet being the result of interference with flow brighteningwhereby the two sides of the sheet tinplate are visibly distinguishablefrom each other.

28. The electrolytic sheet tinplate claimed in claim 24 in which themarking zone covers a minor portion of the entire surface area of thetin coating and the major portion of the entire surface area of the tincoating being outside of the marking zone and having a brightsubstantially mirror-like appearance.

References Cited in the file of this patent UNITED STATES PATENTS779,887 Stewart Jan. 10, 1905 844,380 Marwick Feb. 19, 1907 1,186,217Mark June 6, 1916 14 Bezzenberger Oct. 1, Fernv Dec. 27, Nachtman Apr.29, Hall 1 Feb. 3, Nachtman 2 Aug. 29, Lorig Feb. 15, Munger .1 Dec. 6,Watson Apr. 4, Duby Nov. 27, Netschert Mar. 18, Peters et a1. June 3,Smith Dec. 1,

FOREIGN PATENTS Canada Apr. 23,

